FIG. 1 depicts a portion of the magnetic media 10, which may be a hard disk. The media resides on a substrate 12 and includes a number of layers. A conventional soft underlayer (SUL) 14 and conventional Ta underlayer 16 reside on the substrate 12. The conventional SUL 14 may include multiple layers. Conventional magnetic layers 18 are on the conventional Ta underlayer. For example, a NiW layer 20, a Ru layer 22, and a bottom magnetic layer 24 as well as capping layers 26 and 28. Carbon layer 30 reside on the magnetic layers 18. The first carbon layer 32 may be deposited using chemical vapor deposition (CVD). The top carbon layer 34 may be sputtered. The carbon layers 32 and 34 may be a diamond-like carbon (DLC). The carbon layers 32 and 34 together may form a carbon overcoat layer 30 for the conventional media 10
As part of characterizing the conventional media 10, the conventional carbon overcoat layer 30 is investigated. For example, the thickness of the conventional carbon overcoat layer 30 is desired to be experimentally determined.
FIG. 2 is a flow chart depicting a conventional method 50 for determining the thickness of a carbon layer, such as the conventional carbon overcoat layer 30. For simplicity, some steps are omitted. The carbon layer 30 is exposed to light used for Raman spectroscopy, via step 52. For example, the carbon layer 30 may be exposed by laser light. Light emitted from the carbon layer 30 is detected and used provide a Raman spectrum, via step 54. Typically, the Raman spectrum includes one or more peaks around frequencies specific to the carbon layer 30. Based on the spectrum, the thickness, d, of the carbon layer 30 is determined, via step 56. The spectrum may be curve fitted to determine the contribution of the D and G bands. In particular, the total area of the portion of the Raman spectrum corresponding to the D and G bands (Raman Tarea) may be used to determine the thickness of the conventional carbon overcoat layer 30.
Although the conventional method 50 may be able to determine the thickness for some media, there may be drawbacks. In particular, the Raman Tarea may be affected by layers under the carbon overcoat layer 30. For example, the roughness of films under the carbon overcoat layer 30 may significantly increase the noise in the Raman spectrum. For certain media, such as perpendicular magnetic recording (PMR) media, the contribution of the roughness by the magnetic layers 18 is significant. This noise may change the Raman Tarea calculated and thus the carbon layer thickness determination. As a result, determining the thickness of the carbon layer 30 may be difficult using conventional Raman spectroscopy.